It's not unheard of, unfortunately... are you weighing at the same time every day? Watch out that you aren't weighing after drinking tons of water, or after you eat... could be anything from- the first five pounds you lost purely being water weight, to the six pounds you gained being water weight
Can't let it discourage you, just compare the times you weighed, and what you did differently within the two weigh ins

Actually... When I lost the 5 pounds, I weighed at like 8 in the evening, so I actually had a semi-full stomach. Today I weighed right after getting up..

However... And I just remembered this.. When I had lost, my TOM had just ended the day before... So I maybe could have lost a bunch of water... But.. Why would I have put on a bunch of water all of a sudden?

In order to get the most accurate results and in order to not drive yourself crazy, you MUST weigh at the same time of day, wearing the same clothing. For most people, that's first thing in the morning, naked, maybe before a shower. You've got to be consistient.

Dropping that weight after TOM makes lots of sense. Gaining the 6 lbs kinda makes sense too. You mentioned that you were "not good on your diet for a few days". Well that could do it. It's not automatic. It some times (very often) takes a few days for a "gain" to show up on the scale. Also can take a few days for a "loss" to show. Those 6 lbs were probably the result of the "not so good days" and perhaps a bit of water due to it. Try to keep in mind that it always catches up with us. The good eating (yay!) and the not so good eating (*sigh*).

String together a few more good days and that scale will be on the downslide once again. It's very much about consistiency.

Weight loss is a marathon, not a sprint. Day to day fluctuations will happen ALL THE TIME, and won't always reflect how you did just the previous day. You know you didn't lose weight because you went off plan, right? Or gain because you were on plan?

So stick with your plan and focus on your progress over WEEKS and MONTHS. If daily weigh-ins are messing with your head, only weigh in once a week, at the same time of day.